During various maintenance procedures for a typical nuclear reactor, such as refueling of the reactor core or inspection, the internals structures, which typically take the form of both upper and lower internals, are lifted or removed entirely from within the reactor vessel. Since an operating nuclear reactor generates an irradiated environment, which is safely protected within a typically concrete containment building, borated water or other shielding media is maintained over the irradiated components normally maintained within the interior of the reactor pressure vessel. Power plant personnel during these procedures are usually positioned on an operating deck, which can be about 6 meters (20 feet) above the level of the reactor pressure vessel, to minimize radiation exposure during maintenance procedures. The removal of the internals is often accomplished by a remotely operated lifting rig which is manipulated by the plant's overhead polar crane.
The reactor internals lifting rig is typically a circular structural frame containing bolts which thread into corresponding threaded holes within a radial flange of the reactor internals structures. This is generally done manually through the use of three bolts having long torque tubes which extend upward from the lifting rig to the operating deck. The lifting rig is aligned over the internals by means of bushings on the frame which engage guide studs threaded into the vessel flange after removal of the vessel closure head stud bolts and the vessel closure head.
Several problems may arise in the use of such a prior art device. Over time, during the long operating life of a nuclear power plant, numerous refueling and maintenance operations are normally performed. During these operations the threaded holes within the internals structures can inadvertently become damaged. One possible explanation for this is the fact that personnel must operate from such a remote location. It can be quite difficult, especially because of the presence of the shielding water, to visually verify when the threaded bolts are in the proper position to be threadingly engaged within the internals. Additionally, over torquing of the bolt can cause damage to the threaded sections of the internally threaded holes. Such accidental distortion of the threads can render the conventional lifting rig unusable for the lifting and/or transporting of nuclear reactor internals structures.